Leopard Spots on Mars

In July 2024, NASA’s Perseverance rover was driving through a dried-up river valley in Jezero Crater on Mars. It stopped at a reddish, arrow-shaped rock about a metre long, nicknamed Cheyava Falls. The instruments scanned the surface and found something striking: small dark spots, some tiny like poppy seeds, others larger with pale rings around them. They look almost like leopard print.

The science team spent over a year analysing the data. In September 2025, they published their findings in Nature. Their conclusion, delivered carefully: this rock contains “potential biosignatures.” Features that, on Earth, are most commonly created by living organisms.

To be absolutely clear: this is not a claim that life has been found on Mars. But it is the most compelling evidence to date that microbial life may once have existed there. And the details are remarkable.

What the spots are telling us

The spots aren’t just visual quirks. Perseverance carries two spectrometers (instruments called PIXL and SHERLOC) designed specifically for this kind of chemical detective work. They found a very specific arrangement. The rims of the spots are enriched in iron and phosphorus, in a mineral called vivianite. The cores are enriched in iron and sulphur, in a mineral called greigite. Running through it all: organic carbon, the basic molecular building blocks of life.

What matters isn’t just that these chemicals are present. It’s how they’re arranged. The spots are “reaction fronts”: boundaries where two different chemical environments met. On Earth, microbes thrive at boundaries like these. They pull energy from the minerals around them the way we pull energy from food, and the spots are what’s left behind: the chemical equivalent of crumbs from a very old, very small meal.

Why scientists are excited (but careful)

On Earth, patterns like these in ancient mudstone are almost always biological in origin. The rock itself is made of clay and silt, exactly the sediment that’s best at preserving signs of ancient life. It was deposited in a river valley that once carried water into a lake. Its age (perhaps 2 to 3 billion years old) falls within a window when Mars had liquid water and a thicker atmosphere. Everything about the context says: if Mars ever had life, this is where you’d find the evidence.

But there are non-biological processes that could, in theory, produce similar features. The research team notes these are less likely given the evidence, particularly because the rock shows no signs of being heated to temperatures that would produce these minerals through purely chemical means. The peer-reviewed paper explicitly invites the scientific community to scrutinise the findings. That’s how science is supposed to work: here’s what we found, here’s our best interpretation, now try to prove us wrong.

The definitive answer will likely require bringing the sample home. Perseverance drilled a core from this rock (sample name: Sapphire Canyon) and it’s stored in a sealed tube on the rover, waiting for a future retrieval mission. The rock that might contain evidence of Martian life is sitting on Mars right now, in a tube the size of a marker pen, waiting for someone to come and get it.

Talking about this with your kids

Scientists found polka dots on a rock on Mars. When they looked closely, the dots contained the same chemicals that tiny living things leave behind on Earth. Does that mean something was alive on Mars three billion years ago? Maybe. We won’t know until we bring the rock home and study it properly. Ask your kid: if you could bring one rock home from anywhere in the solar system, which one would you choose, and what would you hope to find inside?

We haven’t found life on Mars. But we may have found the place setting where life once sat down to eat. The plates are still on the table. We just need to go pick them up.

Sources and further reading

NASA/JPL announcement, 10 September 2025: https://www.jpl.nasa.gov

Published in Nature, September 2025: https://www.nature.com

Planetary Society podcast with lead author Joel Hurowitz: https://www.planetary.org/planetary-radio

NPR coverage: https://www.npr.org/2025/09/10